Corvette Tune at Hennessey Performance

Going for a personal best (dyno pull, that is), with help from Hennessey Performance.

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We're at the new shop of John Hennessey and his business partner/CEO Don Goldman in Lake Forest, California, and John's chief calibrator is set to work his magic. Zach "Shaggy" Hill's Acer laptop is wired into my C6 Corvette's central nervous system, and his hands fly over the keyboard in a flurry of taps and clicks. He's playing the EFILive tuning software like a Steinway grand. A tweak to the ignition curve here, an adjustment to the fuel curve there, and horsepower is produced out of thin air—or at least from optimized spark and air/fuel ratio.

Some particulars: The test subject was my own 2005 Chevrolet Corvette, with a 6-speed manual, with gearing exclusive to the Z51 Package. The LS2 6.0-liter V-8 is as stock as the day it rolled off the assembly line, with the exception of an Airraid intake system—a piece I bought as much for appearance as for potential power gain, as the stock dual-filter intake looks a bit clunky. The odometer shows about 18,000 miles—which makes my car a teenager in Corvette years. Last, the tune was done with a tank of 91-octane pump gas, with 85-degree ambient temperature.

The baseline pull on the Dynojet 225 showed some pretty healthy numbers, a peak 346.45 whp (wheel horsepower, as measured at the dyno's roller) and 342.28 lb.-ft. of torque. This jibes with the expected 15-percent loss from the factory 400-bhp figure at the flywheel, the culprits being gear friction, spinning all those driveline bearings, churning up the gear lube, CV joint frictional losses and the rolling resistance of the tires.

Shaggy glances at the readout; more tapping, and three more dyno pulls—the first addressing ignition timing, the last two tweaking the air/fuel ratio. The pulls were done in 4th gear, starting at 2000 rpm through redline, which works out to a speed of 149 mph if the car should suddenly fly off the dyno. Which makes me take two steps back. Considerable fury here, with the exhaust at full song, the tires singing and the car moving around slightly despite the tightly cinched straps, like an ornery rodeo bull still in the gate.

The final numbers? 354.22 whp and 352.41 lb.-ft. of torque, gains of 7.8 and 10.1, respectively. And that's with some heat soak in the equation; the base run was done with a relatively cool engine, so the gains might've been slightly higher for the final pull with an extended cool-down period beforehand. And the horsepower/torque gains are not just bumps or spikes; they're spread quite evenly through the powerband, with the healthiest chunks coming in the very useful range of 4500–5500 rpm. The drive home was a nice validation. In a powerful car it's difficult to feel an additional 8 whp, but what struck me was the extra crispness in throttle response. As fuel is now being burned more efficiently, another benefit should be slightly improved fuel mileage—if I can keep my foot out of the gas. As we all know, that's a big "if." As a final perk, Shaggy was able to electronically eliminate the dreaded Corvette 1-4 skip-shift feature, an ill-conceived fuel-economy Band-Aid and bane to Corvette owners everywhere. Gotta love technology!